Display screen or portion thereof with a graphical user interface for an on-board device



The FIGURE is a front view of a display screen or portion thereof with agraphical user interface for an on-board device, showing our new design.

The outermost rectangle in broken lines shows a display screen or aportion thereof and forms no part of the claimed design. The remainingbroken lines illustrate portions of a graphical user interface and formno part of the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface for an on-board device, as shown anddescribed.